# Type Objects

`PyTypeObject`

  The C structure of the objects used to describe built-in types.

PyObject* `PyType_Type`

  This is the type object for type objects; it is the same object as `type` in the Python layer.

int `PyType_Check`(PyObject *o)

  Return true if the object o is a type object, including instances of types derived from the standard type object. Return false in all other cases.

int `PyType_CheckExact`(PyObject *o)

  Return true if the object o is a type object, but not a subtype of the standard type object. Return false in all other cases.

unsigned int `PyType_ClearCache`()

  Clear the internal lookup cache. Return the current version tag.

unsigned long `PyType_GetFlags`(PyTypeObject* type)

  Return the `tp_flags` member of type. This function is primarily meant for use with Py_LIMITED_API; the individual flag bits are guaranteed to be stable across Python releases, but access to `tp_flags` itself is not part of the limited API.

  New in version 3.2.

  Changed in version 3.4: The return type is now `unsigned long` rather than `long`.

void `PyType_Modified`(PyTypeObject *type)

  Invalidate the internal lookup cache for the type and all of its subtypes. This function must be called after any manual modification of the attributes or base classes of the type.

int `PyType_HasFeature`(PyTypeObject *o, int feature)

  Return true if the type object o sets the feature feature. Type features are denoted by single bit flags.

int `PyType_IS_GC`(PyTypeObject *o)

  Return true if the type object includes support for the cycle detector; this tests the type flag `Py_TPFLAGS_HAVE_GC`.

int `PyType_IsSubtype`(PyTypeObject *a, PyTypeObject *b)

  Return true if a is a subtype of b.

  This function only checks for actual subtypes, which means that `__subclasscheck__()` is not called on b. Call `PyObject_IsSubclass()` to do the same check that `issubclass()` would do.

PyObject* `PyType_GenericAlloc`(PyTypeObject *type, Py_ssize_t nitems)
  Return value: New reference.

  Generic handler for the `tp_alloc` slot of a type object. Use Python’s default memory allocation mechanism to allocate a new instance and initialize all its contents to `NULL`.

PyObject* `PyType_GenericNew`(PyTypeObject *type, PyObject *args, PyObject *kwds)
  Return value: New reference.

  Generic handler for the `tp_new` slot of a type object. Create a new instance using the type’s `tp_alloc` slot.

int `PyType_Ready`(PyTypeObject *type)

  Finalize a type object. This should be called on all type objects to finish their initialization. This function is responsible for adding inherited slots from a type’s base class. Return `0` on success, or return `-1` and sets an exception on error.

void* `PyType_GetSlot`(PyTypeObject *type, int slot)

  Return the function pointer stored in the given slot. If the result is `NULL`, this indicates that either the slot is `NULL`, or that the function was called with invalid parameters. Callers will typically cast the result pointer into the appropriate function type.

  See `PyType_Slot.slot` for possible values of the slot argument.

  An exception is raised if type is not a heap type.

  New in version 3.4.

## Creating Heap-Allocated Types

The following functions and structs are used to create heap types.

PyObject* `PyType_FromSpecWithBases`(PyType_Spec *spec, PyObject *bases)
  Return value: New reference.

  Creates and returns a heap type object from the spec (`Py_TPFLAGS_HEAPTYPE`).

  If bases is a tuple, the created heap type contains all types contained in it as base types.

  If bases is `NULL`, the Py_tp_base slot is used instead. If that also is `NULL`, the new type derives from `object`.

  This function calls `PyType_Ready()` on the new type.

  New in version 3.3.

PyObject* `PyType_FromSpec`(PyType_Spec *spec)
  Return value: New reference.

  Equivalent to `PyType_FromSpecWithBases(spec, NULL)`.

`PyType_Spec`

  Structure defining a type’s behavior.

  const char* `PyType_Spec.name`

    Name of the type, used to set `PyTypeObject.tp_name`.

  int `PyType_Spec.basicsize`
  int `PyType_Spec.itemsize`

    Size of the instance in bytes, used to set `PyTypeObject.tp_basicsize` and `PyTypeObject.tp_itemsize`.

  int `PyType_Spec.flags`

    Type flags, used to set `PyTypeObject.tp_flags`.

    If the `Py_TPFLAGS_HEAPTYPE` flag is not set, `PyType_FromSpecWithBases()` sets it automatically.

  PyType_Slot *`PyType_Spec.slots`

    Array of `PyType_Slot` structures. Terminated by the special slot value `{0, NULL}`.

`PyType_Slot`

  Structure defining optional functionality of a type, containing a slot ID and a value pointer.

  int `PyType_Slot.slot`

    A slot ID.

    Slot IDs are named like the field names of the structures `PyTypeObject`, `PyNumberMethods`, `PySequenceMethods`, `PyMappingMethods` and `PyAsyncMethods` with an added `Py_` prefix. For example, use:

    - `Py_tp_dealloc` to set `PyTypeObject.tp_dealloc`

    - `Py_nb_add` to set `PyNumberMethods.nb_add`

    - `Py_sq_length` to set `PySequenceMethods.sq_length`

    The following fields cannot be set using `PyType_Spec` and `PyType_Slot`:

    - `tp_dict`

    - `tp_mro`

    - `tp_cache`

    - `tp_subclasses`

    - `tp_weaklist`

    - `tp_print`

    - `tp_weaklistoffset`

    - `tp_dictoffset`

    - `bf_getbuffer`

    - `bf_releasebuffer`

    Setting `Py_tp_bases` may be problematic on some platforms. To avoid issues, use the bases argument of `PyType_FromSpecWithBases()` instead.

  void *`PyType_Slot.pfunc`

    The desired value of the slot. In most cases, this is a pointer to a function.

    May not be `NULL`.